1. Field of the Invention
The present invention relates to a method of crystallizing a semiconductor layer, and more specifically, to a method of manufacturing a laterally crystallized semiconductor layer having good electron mobility and good electrical characteristics using a simple, easy process.
2. Description of the Related Art
Transistors are used, for example, as switching devices in flat panel displays (FPDs), such as organic light emitting diodes (OLEDs) or liquid crystal displays (LCDs). In general, a thin film transistor (TFT) comprises a channel area, a source, and a drain formed beside both sides of the channel area, and a gate formed above the channel area.
The channel area in the TFT comprises amorphous silicon or polycrystalline silicon. Polycrystalline silicon (poly-Si) generally has higher mobility than amorphous silicon (a-Si), and thus is advantageous for operating a TFT at high-speed. Amorphous silicon may be crystallized through annealing to obtain polycrystalline silicon, and some electrical characteristics of the channel area are determined by the grain size of the polycrystalline silicon. For example, if the grain size of the polycrystalline silicon is large, the mobility of the electrons becomes greater in the channel area. Thus, some electrical characteristics of the TFT are improved.
Excimer laser annealing (ELA) has been recently used to crystallize amorphous silicon. However, increasing the grain size is limited, i.e., it is difficult to obtain a grain size of 0.5 μm or more, and it is not easy to control uniformity of the grain size.
Accordingly, crystallization methods using sequential lateral solidification (SLS), an optical phase shift mask (OPSM), a pre-patterned laser beam mask (PLBM), or the like, have been suggested. However, the crystallization methods require an apparatus for accurately adjusting substrates and multi-laser beams. Thus, it is very difficult to apply the crystallization methods to a TFT process.